From the related art, an inkjet printer is known (for example, JP-A-2008-213162) which includes a detachable main tank, a sub tank that stores ink supplied from the mounted main tank, and an image recording unit that discharges the ink stored in the sub tank and records an image. Internal spaces of the main tank and the sub tank are opened to the air. For this reason, when the main tank is installed in the inkjet printer, the ink moves so that the liquid level of the main tank and the liquid level of the sub tank are aligned with the same height by the difference between a water head in the internal space of the main tank and a water head in the internal space of the sub tank (hereinafter, referred to as “water head difference”). Thus, when the water head difference becomes almost zero (hereinafter, referred to as “equilibrium state”), the ink movement is stopped.
For example, when the main tank or the sub tank includes a sensor that detects the liquid level, the liquid level of ink in the main tank or the sub tank falls down the detection position, and the user can be notified that the residual amount of ink is low. Further, when the liquid level of ink in the main tank or the sub tank reaches the detection position, counting of the amount of ink discharged from the head is started, and the residual amount of ink in the main tank or the sub tank can be corrected. However, if the liquid level of the ink ascends in an equilibrium state and becomes higher than the detection position after the sensor detects that the liquid level of the ink is lower than the detection position in a state where a water head difference occurs, the detection of the sensor changes. Therefore, the determination result varies depending on the timing at which the sensor signal is determined. On the other hand, since the time until the equilibrium state from when the water head difference occurs varies depending on the amount of ink discharged from the image recording unit, for example, if in a case of determining uniformly the signal of the sensor after a predetermined time has elapsed after the image recording is completed by the image recording unit, the time required for detecting the liquid level of the ink and correcting the residual amount of ink becomes uniformly longer.